The invention relates to a magnetic bubble domain structure comprising a nonmagnetic substrate bearing a bubble domain layer of a soft magnetic material having a positive magnetic anisotropy constant. Magnetic bubble domains can be propagated in the bubble domain layer. The structure further comprises a control layer of a soft magnetic material which is superimposed on the major surface of the bubble domain layer which is remote from the substrate. The control layer defines at least one bubble domain propagation path.
Magnetic bubble domain memories generally comprise one or more memory storage loops, each of which accommodate a number of single-walled magnetic domains. Each magnetic domain represents one binary information bit. These bubble domains are rotated along the loop in a synchronized and controlled manner so as to enable one to access the stored information. See, for example, the article "Bubble memories come to the boil" by P. K. George et al, (Electronics, August 2, 1979, pp. 99-109). A number of different approaches are used in forming the bubble domain propagation paths or circuits.
In so-called "field-access" systems a path or track is usually defined by providing, on the bubble domain layer, a thin film pattern which consists of a series of geometrical forms or elements of a soft magnetic nickel-iron alloy. When an in-plane magnetic driving field is rotated, the elements are polarized successively positively and negatively for propagating or moving, step-by-step the bubble domains along the paths. Bubble domain propagation elements of nickel-iron used so far have, for example, alternate T and I shapes, alternate Y and I shapes, asymmetric chevron shapes, and C-shapes.
However, a disadvantage of the use of such nickel-iron elements is that the magnetostatic interaction ("adhesive force") between bubble domains and elements is so large that undisturbed propagation of bubble domains is possible only with strong rotating fields. This "adhesive force" is related to the fact that a bubble domain magnetizes its surroundings, notably the nickel-iron elements. This is the same effect as a permanent magnet which is laid on an iron table.